Field of the Invention
The present invention relates generally to medical technology, and more specifically to microwave radiation applicators and methods of thermal ablative treatment of tissue using radiated microwaves.
Background Information
Thermal ablative therapies may be defined as techniques that intentionally decrease body tissue temperature (hypothermia) or intentionally increase body tissue temperature (hyperthermia) to temperatures required for cytotoxic effect, or to other therapeutic temperatures depending on the particular treatment. Microwave thermal ablation relies on the fact that microwaves form part of the electromagnetic spectrum causing heating due to the interaction between water molecules and the microwave radiation. The heat being used as the cytotoxic mechanism. Treatment typically involves the introduction or an applicator into tissue, such as tumors. Microwaves are released from the applicator forming a field around its tip. Heating of the water molecules occurs in the radiated microwave field produced around the applicator, rather than by conduction from the probe itself. Heating is therefore not reliant on conduction through tissues, and cytotoxic temperature levels are reached rapidly.
Microwave thermal ablative techniques are useful in the treatment of tumors of the liver, brain, lung, bones, etc.
U.S. Pat. No. 4,494,539 discloses a surgical operation method using microwaves, characterized in that microwaves are radiated to tissue from a monopole type electrode attached to the tip of a coaxial cable for transmitting microwaves. Coagulation, hemostasis or transaction is then performed on the tissue through the use of the thermal energy generated from the reaction of the microwaves on the tissue. In this way, the tissue can be operated in an easy, safe and bloodless manner. Therefore, the method can be utilized for an operation on a parenchymatous organ having a great blood content or for coagulation or transaction on a parenchymatous tumor. According to the method, there can be performed an operation on liver cancer, which has been conventionally regarded as very difficult. A microwave radiation applicator is also disclosed.
U.S. Pat. No. 6,325,796 discloses a microwave ablation assembly and method, including a relatively thin, elongated probe having a proximal access end, and an opposite distal penetration end adapted to penetrate into tissue. The probe defines an insert passage extending therethrough from the access end to the penetration end thereof. An ablation catheter includes a coaxial transmission line with an antenna device coupled to a distal end of the transmission line for generating an electric field sufficiently strong enough to cause tissue ablation. The coaxial transmission line includes an inner conductor and an outer conductor separated by a dielectric material. A proximal end of the transmission line is coupled to a microwave energy source. The antenna device and the transmission line each have a transverse cross-sectional dimension adapted for sliding receipt through the insert passage while the elongated probe is positioned in the tissue. Such sliding advancement continues until the antenna device is moved to a position beyond the penetration end and further into direct contact with the tissue.
However, a drawback with the existing techniques include the fact that they are not optimally mechanically configured for insertion into and perforation of, the human skin, for delivery to a zone of soft tissue to be treated. Typically, known radiation applicator systems do not have the heightened physical rigidity that is desirable when employing such techniques.
In addition, some radiation applicators made available heretofore do not have radiation emitting elements for creating a microwave field pattern optimized for the treatment of soft tissue tumors.
Also, given the power levels employed in some applicators and treatments, there can be problems of unwanted burning of non-target, healthy tissue due to the very high temperatures reached by the applicator or the components attached thereto.
Further, although small diameter applicators are known, and liquid cooling techniques have been used, there has been difficulty in designing a small diameter device with sufficient cooling in applications employing power levels required to deal with soft tissue tumors.
Accordingly, there is a need for methods of treatment of soft tissue tumors, and for radiation applicators that overcome any or all of the aforementioned problems of the prior art techniques, and provide improved efficacy.